Lila Thompson is a Ph.D. candidate in computer science at Stanford University and the founding president of the Public Communication for Researchers initiative.
The 1990s were a chaotic era. There was Crystal Pepsi, the Macarena, and who could forget Tickle Me Elmo? But one of the most exasperating memories I have is the painfully slow Internet. Whenever I needed to email a PowerPoint presentation for school, I would connect my modem, endure the beeping and whistling, initiate the upload, and then head off to dinner, hoping that by the time I returned, my email had finally sent.
However, I had an ace up my sleeve for those urgent situations: file compression, known as “zipping.” Programs like WinZip could take an 80 MB PowerPoint file, work its magic, and shrink it to a ZIP file that retained all the original data, reduced to just one-third of its size.
Initially, I didn’t think much of this trick, but as I pondered it further, it felt like a form of sorcery. The file was smaller, yet no data was genuinely lost, as the recipient could effortlessly recreate the original. It was as if you could fit a 6-foot package into a 2-foot box for shipping and then retrieve the original once it reached its destination. So, where did all that data go in the meantime?
Deflating the Package
The analogy of a package hints at a potential explanation. Just like you could compress a package containing an inflatable object—say, a large beach ball—by deflating it, computers also find ways to eliminate unnecessary data. But unlike the ball, which contains mostly air, I would be quite upset if WinZip started erasing parts of my carefully crafted presentation. So, what is the “air” that can be extracted from a PowerPoint file?
Computers deploy techniques similar to those we humans use to process information. Imagine, for example, a snare drummer preparing to play Ravel’s renowned “Boléro.” With 4,050 drumbeats to keep track of, that’s a lot of timing to remember! However, the snare part is surprisingly redundant, repeating a single sequence of 24 beats continuously until the very end. This means that instead of memorizing every note, the drummer can simply remember “chunk chunk chunk…”
This process mirrors how file compression works. Just as a musician identifies patterns in music, a compression program seeks out repeating sequences throughout a file and condenses them into shorthand. For example, if my school presentation included the classic tongue-twister, “How much wood could a woodchuck chuck if a woodchuck could chuck wood?” (yes, I was a peculiar child), the program would recognize the repeated words and replace them with symbols like “X,” “Y,” and “Z.” These redundant parts are the “air” that gets removed from the document.
Of course, the recipient’s computer also needs to understand what each shorthand means. Thus, the compression program saves a symbol table to reconstruct the original file, much like instructions for reinflating the beach ball.
Balancing Redundancy
Redundancy not only explains the puzzle of compression but also highlights opportunities for even greater data savings. Our tendency to share large media files, such as songs and videos, is made possible by clever techniques that further reduce redundancy. However, this raises another question: if there’s so much redundancy, why do my original PowerPoint files seem excessively large?
The creators of PowerPoint were certainly aware of the possibility of compressing files, but size was not their only consideration. Imagine how inconvenient it would be if you had to inflate your beach ball every time you wanted to use it! This scenario mirrors the tradeoff between space efficiency and convenience that we encounter in our daily lives. You could calculate how many cups are in a pint every time you cook, but it’s often easier to memorize it. Similarly, if your computer required decompressing a file for every action, it would feel like returning to the slow Internet days. Maintaining some redundancy means more data but significantly less hassle.
For both computers and humans, finding the right balance of redundancy is essential. Too little redundancy forces constant re-derivation of information, while too much can overwhelm your internet connection—think of a streaming video saturating your bandwidth.
Fortunately, this balance is generally achieved. It’s through a combination of redundancy and compression that I can download a copy of “The Shawshank Redemption” and watch it seamlessly on my laptop. Oh, and “Braveheart,” “The Matrix,” and “Schindler’s List” too. Maybe the ’90s weren’t so terrible after all.
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Summary:
This article explores the fascinating mechanism of file compression, comparing it to the cognitive strategies we use to process information. By identifying and eliminating redundancy, computers can significantly reduce file sizes while retaining all necessary data—just like a deflated beach ball fits neatly in a smaller box. The balance between efficiency and convenience is essential for both technology and human memory.